Swift Heavy Ion Irradiation of Pressurized Boron Nitride

Recently, it has been shown that irradiation with swift heavy ions can trigger [1] or also prevent [2] phase transitions in oxides at static high pressure and outside the equilibrium stability field [3]. At GSI, several experiments were conducted in order to probe the influence of applied pressure of up to 25 GPa on the irradiation behaviour of various materials [2, 3]. We decided to study effects of elevated pressure and simultaneous ion irradiation on boron nitride (BN), the reason being its simple structure, the structural relationship to the carbon allotropes, the existing knowledge about polymorphism, and the technical relevance of this material class. Transformations between hexagonal, cubic, rhombohedral and wurtzitic BN (hBN, cBN, rBN, wBN) in the pressure-temperature parameter space are well established [4, 5]. Our focus is the transformation of hBN to wBN, which is supposed to be quenchable only in nanostructured material [4].